Magnetic resonance imaging apparatus and magnetic resonance imaging method

ABSTRACT

A magnetic resonance imaging apparatus includes an imaging unit which applies a labeling pulse to invert a spin included in a labeling region within part of a imaging region and then collects a echo signal from a time point when an inversion time has passed from the application of the labeling pulse, and a control unit, the control unit controlling the imaging unit so that the echo signal in the imaging region is collected a plurality of times with variations in the inversion time, the control unit also controlling the imaging unit so that a time ranging from a reference time point within a biological signal obtained from a subject to the application of the labeling pulse is a time determined in accordance with the inversion time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of Ser. No. 11/898,110 filed Sep. 10,2007, now U.S. Pat. No. ______, which is based upon and claims thebenefit of priority from prior Japanese Patent Application No.2006-248541, filed Sep. 13, 2006, the entire contents of both of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic resonance imaging apparatusand a magnetic resonance imaging method suited to an observation of thedynamic state of a moving material in a body such as blood orcerebrospinal fluid (CSF).

2. Description of the Related Art

A method has been known wherein inversion pulses are applied in order tolabel, in the form of longitudinal magnetization, an observation targetlocated in a position at a time, and an MRI image is taken after a giventime, thereby recognizing the distribution of the labeled observationtarget (e.g., refer to “Considerations of Magnetic Resonance Angiographyby Selective Inversion Recovery,” D. G. Nishimura et al., MagneticResonance in Medicine, Vol. 7, pages 472-484 (1988)).

In the case where this method is used, in general, a time when acharacteristic electrocardiographic waveform such as an R wave emergesis set as a reference so that RF excitation and echo signal collectionfor imaging are carried out at a time when a certain amount of time haspassed from the above-mentioned time. This utilizes the nature of theflow velocity change of, for example, blood or cerebrospinal fluid thatoften highly correlates with a cardiac phase. Such a synchronizationmethod is employed because artifacts due to pulsation can be reduced,because the capability to visualize, for example, the blood orcerebrospinal fluid and signal strength are stabilized, and becauseimage quality is improved.

Another method has been known that conducts labeling for longitudinalmagnetization by a selective excitation method before echo signalcollection for imaging, and takes a plurality of images with variationsin an inversion time TI ranging from the time of the labeling to theimaging (e.g., refer to Japanese Patent Application KOKAI PublicationNo. 2001-252263). The plurality of images obtained by this method issequentially displayed at regular intervals such that it is possible toobserve the dynamic state of a moving material in a body such as theblood or cerebrospinal fluid.

FIG. 24 is a diagram showing a pulse sequence of this prior art example.Waveforms shown in FIG. 24 represent, from top to bottom, anelectrocardiograph (ECG) as a synchronization waveform, aradio-frequency (RF) pulse applied to an imaging target, a slicedirection gradient magnetic field waveform (Gss), a readout directiongradient magnetic field waveform (Gro), a phase encoding directiongradient magnetic field waveform (Gpe), and a deviation (a) of a carrierwave from a center frequency during the application of theradio-frequency pulse. A period P1 is a tag (label) sequence part forlabeling the blood or cerebrospinal fluid, and a period P2 is a mainpulse sequence part for imaging. For periods P1 and P2, a combination ofgradient magnetic field strengths and Δf can be independently set at thetime of the selective excitation, and the direction and position of anexcited surface can be independently set. Although a case of a fast spinecho method is shown in this example, it is possible to use any imagingmethod such as a coherent gradient echo method (a true SSFP method, trueFISP or balanced FFE method). The number of shots necessary toreconstruct one image is collected during the same inversion time TI.The imaging is repeated with variations in this inversion time TI. Aplurality of images taken at different inversion times TI aresequentially displayed to enable the observation of the dynamic state ofthe cerebrospinal fluid. With regard to parts with motion among partsexcited by a labeling pulse LP in period P1, portions outside a labelingregion show a low signal intensity on the image because of motioncorresponding to a flow velocity during the inversion time TI. Thispermits the observation of the motion of the blood or cerebrospinalfluid. Another example has been shown wherein one more nonselective IRpulse is added before or after an RF pulse in period P1 in terms of timesuch that the longitudinal magnetization of the labeled part issubstantially brought to an initial state, thereby imaging the motion ofthe blood or cerebrospinal fluid as a high signal intensity.

As measurement means for the motion of the cerebrospinal fluid, thereare also known, for example, a method wherein a radioisotope is injectedinto a spinal cavity and its motion in a body is traced by several hoursby means such as a scintillation counter, and a method that uses acontrast media (metrizamide) to perform a measurement in the same mannerby X-ray computed tomography (CT). In spite of an advantage offacilitating the observation of the long-time motion called bulk motionof the cerebrospinal fluid, all of these methods entail a high degree ofinvasiveness of a test subject. Moreover, since the radioisotope orcontrast media is injected in these methods, the inner pressure of thecerebrospinal fluid might change, which affects an observation target.

First Problem: if the inversion time TI is changed, a time from areference time point to imaging (times TDseq1, TDseq2 in FIG. 24)changes as much as the change of the inversion time TI in the case wherethe method shown in Japanese Patent Application KOKAI Publication No.2001-252263 is used to observe the dynamic state of the blood orcerebrospinal fluid. Thus, the flow velocity of the blood orcerebrospinal fluid during collection varies every imaging, so thatthere is a disadvantage that a signal value changes due to effects otherthan the difference of the inversion time TI or the capability tovisualize the blood or cerebrospinal fluid varies every imaging.Especially when, for example, a fast spin echo method is employed thatuses a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence as a main pulsesequence, an image is formed as the composition of a plurality of echocomponents with different phase variations due to flow Velocities, andthis leads to sharp changes in image values corresponding to the flowvelocities due to the interferential action of phases, which is aserious problem.

Second Problem: in the case where the imaging target is thecerebrospinal fluid, the correlation with the cardiac phase is notnecessarily high, and the pulsation regularity of the cerebrospinalfluid tends to be lower than that of blood. Therefore, in the case ofthe observation target such as the cerebrospinal fluid, there has been adisadvantage that it is not easy to judge whether a change is caused byindividual imaging variations or by the variation of the inversion timeTI, even if images with the sequentially changed inversion time TI arecompared.

Third Problem: in normal labeling methods, there has been a disadvantagethat it is not easy to know the motion of the cerebrospinal fluid orblood in the whole two- or three-dimensional region because the labelingregion is limited to a straight form.

Fourth Problem: when an imaging section is set out of a normalpositioning image, it is not easy to set a labeling region at a properposition because a portion with a suspected lesion of the blood orcerebrospinal fluid is unclear on the positioning image for labeling,and there has been a disadvantage that it is not easy to visualize themotion of the cerebrospinal fluid or blood.

Fifth Problem: there has been a disadvantage that clinical knowledge ofthe circulatory pathways of the cerebrospinal fluid or blood is requiredfor a user of an apparatus in order to carry out the imaging usinglabeling, and properly setting imaging conditions is difficult.

BRIEF SUMMARY OF THE INVENTION

Under such circumstances, it has been firstly desired to be able toobtain an image that accurately indicates a change of a signal valuewith the difference of an inversion time TI and that visualizes a movingmaterial with a stable visualization capability.

It has been secondly desired to be able to obtain a plurality of imagesthat visualize the moving material with timings synchronized with itspulsation to a high degree.

It has been thirdly desired to be able to obtain an image useful to knowthe motion of the moving material from more sides.

It has been fourthly desired to be able to easily set a labeling region.

It has been fifthly desired to be able to easily and properly setimaging conditions.

According to a first aspect of the present invention, there is provideda magnetic resonance imaging apparatus that generates a magneticresonance image on the basis of an echo signal regarding a spin includedin an imaging region of a subject, the apparatus comprising: an imagingunit that applies a labeling pulse to invert the spin included in alabeling region within part of the imaging region and then collects theecho signal from a time point when an inversion time has passed from theapplication of the labeling pulse; and a control unit, the control unitcontrolling the imaging unit so that the echo signal in the imagingregion is collected a plurality of times with variations in theinversion time, the control unit also controlling the imaging unit sothat a time ranging from a reference time point within a biologicalsignal obtained from the subject to the application of the labelingpulse is a time determined in accordance with the inversion time.

According to a second aspect of the present invention, there is provideda magnetic resonance imaging apparatus that generates a magneticresonance image on the basis of an echo signal regarding a spin includedin an imaging region of a subject, the apparatus comprising: an imagingunit that applies a labeling pulse to invert the spin included in alabeling region within part of the imaging region and then applies anexcitation pulse at a time point when an inversion time has passed fromthe application of the labeling pulse in order to collect the resultingecho signal; and a control unit, the control unit controlling theimaging unit so that the echo signal in the imaging region is collecteda plurality of times with variations in the inversion time, the controlunit also controlling the imaging unit so that a time ranging from areference time point within a biological signal obtained from thesubject to the application of the excitation pulse is constantregardless of the inversion time in the plurality of collections of theecho signal.

According to a third aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: an acquisition unitthat acquires an echo signal regarding a spin included in an imagingregion of a subject in accordance with a predetermined pulse sequence; areconstruction unit that reconstructs an image of the inside of theimaging region in accordance with the acquired echo signal; a labelingunit that inverts the spin included in a labeling region within part ofthe imaging region to conduct labeling; and a control unit, the controlunit controlling the labeling unit and the acquisition unit so that acycle of conducting the labeling and acquiring the echo signal from atime point when a first time has passed from a time point of thelabeling is carried out a plurality of times with variations in thefirst time, the control unit also controlling the labeling unit and theacquisition unit so that each of the plurality of cycles is started at atime point when a second time that increases or decreases contrary tothe size of the first time in each cycle has passed from a periodicreference time point.

According to a fourth aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: an acquisition unitthat acquires an echo signal regarding a spin included in an imagingregion of a subject in accordance with a predetermined pulse sequence; areconstruction unit that reconstructs an image of the inside of theimaging region in accordance with the acquired echo signal; a labelingunit that inverts the spin included in a labeling region within part ofthe imaging region to conduct labeling; and a control unit, the controlunit controlling the labeling unit and the acquisition unit so that acycle of conducting the labeling and acquiring the echo signal from atime point when a given first time has passed from a time point of thelabeling is carried out a plurality of times without changing thelabeling region, the control unit also controlling the labeling unit andthe acquisition unit so that each of the plurality of cycles is startedat a time point when a given second time has passed from a periodicreference time point.

According to a fifth aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: an acquisition unitthat acquires an echo signal regarding a spin included in an imagingregion of a subject in accordance with a predetermined pulse sequence; areconstruction unit that reconstructs an image of the inside of theimaging region in accordance with the acquired echo signal; a labelingunit that inverts the spin included in a labeling region within part ofthe imaging region to conduct labeling; an observation unit thatrepetitively acquires a magnetic resonance signal from within thelabeling region and observes a change of the flow velocity of a fluid inthe labeling region on the basis of a change of the repetitivelyacquired magnetic resonance signal; and a control unit, the control unitcontrolling the labeling unit and the acquisition unit so that a cycleof conducting the labeling and acquiring the echo signal from a timepoint when a predetermined first time has passed after the labeling iscarried out a plurality of times, the control unit also controlling thelabeling unit and the acquisition unit so that the cycle is started at atime point when a predetermined second time has passed from a referencetime point at which the observed change of the flow velocity coincideswith a predetermined state.

According to a sixth aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: an acquisition unitthat acquires an echo signal regarding a spin included in an imagingregion of a subject in accordance with a predetermined pulse sequence; areconstruction unit that reconstructs an image of the inside of theimaging region in accordance with the acquired echo signal; a labelingunit that inverts the spin included in the imaging region and theninverts the spin included in each of a plurality of labeling regionswithin part of the imaging region to conduct labeling; and a controlunit, the control unit controlling the labeling unit and the acquisitionunit so that a cycle of conducting the labeling and acquiring the echosignal from a time point when a predetermined first time has passed froma time point of the labeling is carried out a plurality of times, thecontrol unit also controlling the labeling unit and the acquisition unitso that the cycle is started at a time point when a predetermined secondtime has passed from a periodic reference time point.

According to a seventh aspect of the present invention, there isprovided a magnetic resonance imaging apparatus comprising: anacquisition unit that acquires an echo signal regarding a spin includedin an imaging region of a subject in accordance with a predeterminedpulse sequence; a reconstruction unit that reconstructs an image of theinside of the imaging region in accordance with the acquired echosignal; a labeling unit that inverts the spin included in a labelingregion within part of the imaging region to conduct labeling; a controlunit, the control unit controlling the labeling unit and the acquisitionunit so that a cycle of conducting the labeling and acquiring the echosignal from a time point when a predetermined first time has passedafter the labeling is carried out a plurality of times, the control unitalso controlling the labeling unit and the acquisition unit so that eachof the plurality of cycles is started at a time point when apredetermined second time has passed from a periodic reference timepoint; a unit that displays, as a positioning image, one of theplurality of images reconstructed on the basis of the echo signalacquired in each of the plurality of cycles; and a unit that accepts adesignation of an imaging section on the positioning image.

According to an eighth aspect of the present invention, there isprovided a magnetic resonance imaging apparatus having access to astorage device, the apparatus comprising: an acquisition unit thatacquires an echo signal regarding a spin included in an imaging regionof a subject in accordance with a predetermined pulse sequence; areconstruction unit that reconstructs an image of the inside of theimaging region in accordance with the acquired echo signal; a labelingunit that inverts the spin included in a labeling region within part ofthe imaging region to conduct labeling; a control unit, the control unitcontrolling the labeling unit and the acquisition unit so that a cycleof conducting the labeling and acquiring the echo signal from a timepoint when a predetermined first time has passed after the labeling iscarried out a plurality of times, the control unit also controlling thelabeling unit and the acquisition unit so that each of the plurality ofcycles is started at a time point when a predetermined second time haspassed from a periodic reference time point; and a unit that sets thelabeling region on the basis of information stored in the storagedevice.

According to a ninth aspect of the present invention, there is provideda magnetic resonance imaging method that generates a magnetic resonanceimage on the basis of an echo signal regarding a spin included in animaging region of a subject, the method comprising: applying a labelingpulse to invert the spin included in a labeling region within part ofthe imaging region and then collecting the echo signal from a time pointwhen an inversion time has passed from the application of the labelingpulse; and collecting the echo signal in the imaging region a pluralityof times with variations in the inversion time, and also controlling theapplication of the labeling pulse and the collection so that a timeranging from a reference time point within a biological signal obtainedfrom the subject to the application of the labeling pulse is a timedetermined in accordance with the inversion time.

According to a tenth aspect of the present invention, there is provideda magnetic resonance imaging method that generates a magnetic resonanceimage on the basis of an echo signal regarding a spin included in animaging region of a subject, the method comprising: applying a labelingpulse to invert the spin included in a labeling region within part ofthe imaging region and then applying an excitation pulse at a time pointwhen an inversion time has passed from the application of the labelingpulse in order to collect the resulting echo signal; and controlling theapplication of the labeling pulse and the collection so that the echosignal in the imaging region is collected a plurality of times withvariations in the inversion time, and also controlling the applicationof the labeling pulse and the collection so that a time ranging from areference time point within a biological signal obtained from thesubject to the application of the excitation pulse is constantregardless of the inversion time in the plurality of collections of theecho signal.

According to a eleventh aspect of the present invention, there isprovided a magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; reversing the spinincluded in a labeling region within part of the imaging region toconduct labeling; controlling the labeling and the acquisition so that acycle of conducting the labeling and acquiring the echo signal from atime point when a first time has passed from a time point of thelabeling is carried out a plurality of times with variations in thefirst time, and also controlling the labeling and the acquisition sothat each of the plurality of cycles is started at a time point when asecond time that increases or decreases contrary to the size of thefirst time in each cycle has passed from a periodic reference timepoint; and reconstructing an image of the inside of the imaging regionin accordance with the acquired echo signal.

According to a twelfth aspect of the present invention, there isprovided a magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; reversing the spinincluded in a labeling region within part of the imaging region toconduct labeling; controlling the labeling and the acquisition so that acycle of conducting the labeling and acquiring the echo signal from atime point when a given first time has passed from a time point of thelabeling is carried out a plurality of times without changing thelabeling region, and also controlling the labeling and the acquisitionso that each of the plurality of cycles is started at a time point whena given second time has passed from a periodic reference time point; andreconstructing an image of the inside of the imaging region inaccordance with the acquired echo signal.

According to a thirteenth aspect of the present invention, there isprovided a magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; reversing the spinincluded in a labeling region within part of the imaging region toconduct labeling; repetitively acquiring a magnetic resonance signalfrom within the labeling region and observing a change of the flowvelocity of a fluid in the labeling region on the basis of a change ofthe repetitively acquired magnetic resonance signal; controlling thelabeling and the acquisition so that a cycle of conducting the labelingand acquiring the echo signal from a time point when a predeterminedfirst time has passed after the labeling is carried out a plurality oftimes, and also controlling the labeling and the acquisition so that thecycle is started at a time point when a predetermined second time haspassed from a reference time point at which the observed change of theflow velocity coincides with a predetermined state; and reconstructingan image of the inside of the imaging region in accordance with theacquired echo signal.

According to a fourteenth aspect of the present invention, there isprovided a magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; reversing the spinincluded in the imaging region and then reversing the spin included ineach of a plurality of labeling regions within part of the imagingregion to conduct labeling; and controlling the labeling and theacquisition so that a cycle of conducting the labeling and acquiring theecho signal from a time point when a predetermined first time has passedfrom a time point of the labeling is carried out a plurality of times,and also controlling the labeling and the acquisition so that the cycleis started at a time point when a predetermined second time has passedfrom a periodic reference time point; reconstructing an image of theinside of the imaging region in accordance with the acquired echosignal.

According to a fifteenth aspect of the present invention, there isprovided a magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; reversing the spinincluded in a labeling region within part of the imaging region toconduct labeling; controlling the labeling and the acquisition so that acycle of conducting the labeling and acquiring the echo signal from atime point when a predetermined first time has passed after the labelingis carried out a plurality of times, and also controlling the labelingand the acquisition so that each of the plurality of cycles is startedat a time point when a predetermined second time has passed from aperiodic reference time point; reconstructing an image of the inside ofthe imaging region in accordance with the acquired echo signal;displaying, as a positioning image, one of the plurality of imagesreconstructed on the basis of the echo signal acquired in each of theplurality of cycles; and accepting a designation of an imaging sectionon the positioning image.

According to a sixteenth aspect of the present invention, there isprovided a magnetic resonance imaging method in a magnetic resonanceimaging apparatus having access to a storage device, the methodcomprising: acquiring an echo signal regarding a spin included in animaging region of a subject in accordance with a predetermined pulsesequence; reversing the spin included in a labeling region within partof the imaging region to conduct labeling; controlling the labeling andthe acquisition so that a cycle of conducting the labeling and acquiringthe echo signal from a time point when a predetermined first time haspassed from a time point of the labeling is carried out a plurality oftimes, and also controlling the labeling and the acquisition so thateach of the plurality of cycles is started at a time point when apredetermined second time has passed from a periodic reference timepoint; setting the labeling region on the basis of information stored inthe storage device; and reconstructing an image of the inside of theimaging region in accordance with the acquired echo signal.

Additional objects and advantages of the invention will be set forth inthe description that follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a diagram showing the configuration of a magnetic resonanceimaging apparatus according to first to seventh embodiments of thepresent invention;

FIG. 2 is a diagram showing a pulse sequence in a first embodiment;

FIG. 3 is a flowchart for the processing of a host computer in FIG. 1for condition setting;

FIG. 4 is a diagram showing a modification of the pulse sequence in thefirst embodiment;

FIG. 5 is a diagram showing a pulse sequence in a second embodiment;

FIG. 6 is a diagram showing a pulse sequence for trigger detection in aperiod P11 in FIG. 5;

FIG. 7 is a diagram showing one example of a waveform of an echo signalobtained by the pulse sequence for trigger detection, and profiles of anabsolute value and a phase in a readout direction obtained byone-dimensional Fourier transformation of the echo signal;

FIG. 8 is a diagram in which a phase change θ(ro, i) measured by thepulse sequence for trigger detection is plotted in order of time;

FIG. 9 is a diagram showing an example of how an excitation region andan observation region are set in the second embodiment;

FIG. 10 is a diagram showing another example of how the excitationregion and the observation region are set in the second embodiment;

FIG. 11 is a diagram showing a pulse sequence in a third embodiment;

FIG. 12 is a diagram showing how images IM1, IM2, . . . , IMm areaveraged to generate an average image IMave;

FIG. 13 is a diagram showing how to generate a variance image IMvarproportionate to the variance of the images IM1, IM2, . . . , IMm;

FIG. 14 is a diagram showing a pulse sequence in a fourth embodiment;

FIG. 15 is a diagram showing an example of how a labeling region is setin the fourth embodiment;

FIG. 16 is a diagram explaining one example of a section suitable toobtaining a positioning image for setting the labeling region in thefourth embodiment;

FIG. 17 is a diagram showing a two-dimensional image taken in a sectionS1 shown in FIG. 16 and an example of how to set labeling regions inthis image;

FIG. 18 is a diagram showing one example of an image taken by the pulsesequence in the fourth embodiment when labeling regions R11 and R12 areset as shown in FIG. 17;

FIG. 19 is a diagram showing one example of a positioning image in afifth embodiment;

FIG. 20 is a diagram showing an example of how o set an imaging sectionon the positioning image shown in FIG. 19;

FIG. 21 is a diagram showing a two-dimensional image taken in a sectionS11 shown in FIG. 20; FIG. 22 is a diagram showing one example of animage obtained by imaging after labeling a labeling region R23 as shownin FIG. 21;

FIG. 23 is a flowchart for the characteristic processing of a hostcomputer 6 in FIG. 1 in a sixth embodiment; and

FIG. 24 is a diagram showing a pulse sequence disclosed in JapanesePatent Application KOKAI Publication No. 2001-252263.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, first to seventh embodiments of the present invention willbe described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a magnetic resonanceimaging apparatus (hereinafter referred to as an MRI apparatus) 100according to the first to seventh embodiments.

The MRI apparatus 100 comprises a bed on which a subject 200 is mounted,a static magnetic field generator for generating a static magneticfield, a gradient magnetic field generator for adding positionalinformation to the static magnetic field, a transmitter/receiver fortransmitting/receiving a high-frequency signal, and acontroller/computer responsible for the control of the whole system andimage reconstruction. As components of these parts, the MRI apparatus100 has a magnet 1, a static power supply 2, a gradient coil unit 3, agradient power supply 4, a sequencer (sequence controller) 5, a hostcomputer 6, an RF coil unit 7, a transmitter 8T, a receiver 8R, aarithmetical unit 10, a storage unit 11, a display 12, an input unit 13,a shim coil 14 and a shim power supply 15. The MRI apparatus 100 furthercomprises an electrocardiographic measure for measuring an ECG signal asa signal indicating a cardiac phase of the subject 200, a breath-holdinginstructor for instructing the subject 200 to hold breath. Components ofthe electrocardiographic measure and the breath-holding instructorinclude a sound generator 16, an ECG sensor 17 and an ECG unit 18.

The static magnetic field generator includes the magnet 1 and the staticpower supply 2. For example, a superconducting magnet or a normalconducting magnet can be used as the magnet 1. The static power supply 2supplies a current to the magnet 1. Thus, the static magnetic fieldgenerator generates a static magnetic field B₀ in a cylindrical space(diagnostic space) into which the subject 200 is sent. The direction ofthis static magnetic field B₀ substantially coincides with the axialdirection (Z axis direction) of the diagnostic space. The staticmagnetic field generator is further provided with the shim coil 14. Thisshim coil 14 is supplied with a current from the shim power supply 15under the control of the host computer 6 and generates a correctingmagnetic field for homogenizing the static magnetic field.

The bed sends a top board on which the subject 200 is mounted into thediagnostic space or pulls it out of the diagnostic space.

The gradient magnetic field generator includes the gradient coil unit 3and the gradient power supply 4. The gradient coil unit 3 is disposedinside the magnet 1. The gradient coil unit 3 comprises three sets ofcoils 3 x, 3 y and 3 z for generating gradient magnetic fields in the Xaxis direction, Y axis direction and Z axis direction that areperpendicular to each other. The gradient power supply 4 supplies pulsecurrents for generating the gradient magnetic fields in the coils 3 x, 3y and 3 z under the control of the sequencer 5. Thus, the gradientmagnetic field generator controls the pulse currents supplied from thegradient power supply 4 to the coils 3 x, 3 y and 3 z to synthesize thegradient magnetic fields in the directions of the three axes (X axis, Yaxis and Z axis) that are physical axes, thereby arbitrarily settinggradient magnetic fields in logical axis directions including slicedirection gradient magnetic field Gss, a phase encoding directiongradient magnetic field Gpe and readout direction (frequency encodingdirection) gradient magnetic field Gro that are perpendicular to eachother. The gradient magnetic fields Gss, Gpe and Gro in the slicedirection, phase encoding direction and readout direction are superposedon the static magnetic field B₀.

The transmitter/receiver includes the RF coil unit 7, the transmitter 8Tand the receiver 8R. The RF coil unit 7 is disposed in the vicinity ofthe subject 200 in the diagnostic space. The transmitter 8T and thereceiver 8R are connected to the RF coil unit 7. The transmitter 8T andthe receiver 8R operate under the control of the sequencer 5. Thetransmitter 8T supplies RF current pulses at Larmor frequency forcausing nuclear magnetic resonance (NMR) to the RF coil unit 7. Thereceiver 8R imports an MR signal (high-frequency signal) such as an echosignal received by the RF coil unit 7, and subjects it to various signalprocessing such as preamplification, intermediate frequency conversion,phase detection, low-frequency amplification and filtering, and thensubjects the signal to A/D conversion to generate echo data (raw data)in a digital quantity corresponding to the echo signal.

The controller/computer includes the sequencer 5, the host computer 6,the arithmetical unit 10, the storage unit 11, the display 12 and theinput unit 13.

The sequencer 5 comprises a CPU and a memory. The sequencer 5 storespulse sequence information sent from the host computer 6 in the memory.The CPU of the sequencer 5 controls the operations of the gradient powersupply 4, the transmitter 8T and the receiver 8R in accordance with thesequence information stored in the memory, and also temporarily inputsthe echo data output by the receiver 8R and transfers it to thearithmetical unit 10. Here, the sequence information is the wholeinformation necessary to operate the gradient power supply 4, thetransmitter 8T and the receiver 8R in accordance with a series of pulsesequences, and includes information regarding, for example, theintensity of the pulse currents applied to the coils 3 x, 3 y and 3 z,application time, and application timing.

The host computer 6 has various functions achieved by carrying out apredetermined software procedure. One of the functions is to instructthe sequencer 5 on the sequence information and perform the overallcontrol of the operation of the whole apparatus. One of the functions isto control the sequencer 5 to collect the echo signals in an imagingregion a plurality of times with a varying inversion time, and tocontrol the sequencer 5 so that a time from a reference time point inthe ECG signal to the application of labeling pulses may be a propertime. Further, functions provided in the host computer can include thefollowing functions. One of the functions is to repetitively acquire amagnetic resonance signal from within a labeling region, and observe thechange of the flow velocity of a fluid in the labeling region on thebasis of the change of the repetitively acquired magnetic resonancesignal. One of the functions is to display one of a plurality of imagesreconstructed on the basis of the echo signals acquired by the pluralityof collections, as a positioning image o on the display 12. One of thefunctions is to accept the designation of an imaging section on thepositioning image. One of the functions is to set the labeling region onthe basis of the information stored in the storage unit 11.

The host computer 6 performs an imaging scan after preparatory taskssuch as a positioning scan. The imaging scan is a scan for collecting aset of echo data necessary for the image reconstruction, and is set hereto a two-dimensional scan. The imaging scan can be performed incombination with an ECG gate method based on the ECG signal. Inaddition, this ECG gate method does not have to be used in combinationin some cases.

The pulse sequence includes a three-dimensional (3D) or two-dimensional(2D) scan. For the form of its pulse train, use is made of, for example,a spin echo (SE) method, a fast spin echo (FSE) method, a fastasymmetric spin echo (FASE) method that is a combination of the fast SEmethod and a half-Fourier method, or an echo planar imaging (EPI)method.

The echo data output by the receiver 8R is input to the arithmeticalunit 10 through the sequencer 5. The arithmetical unit 10 disposes theinput echo data in a Fourier space (also referred to as a k space or afrequency space) set in an internal memory. The arithmetical unit 10subjects the echo data disposed in the Fourier space to two- orthree-dimensional Fourier transformation to reconstruct real-space imagedata. The arithmetical unit 10 can also perform synthesizing processingand difference computing processing for data on the image as necessary.

The synthesizing processing includes, for example, addition processingfor adding image data for a plurality of two-dimensional frames withrespect to each corresponding pixel, and maximum intensity projection(MIP) processing or minimum intensity projection processing forselecting a maximum value or minimum value in a sight line direction forthree-dimensional data. Another example of the synthesizing processingmay be to align the axes of a plurality of frames on the Fourier spaceto synthesize them with the echo data for one frame without changing theecho data. In addition, the addition processing includes simple additionprocessing, averaging processing, weighting addition processing, etc.

The storage unit 11 stores the reconstructed image data and the imagedata subjected to the above-mentioned synthesizing processing anddifference processing.

The display 12 indicates various images to be presented to a user underthe control of the host computer 6. A display device such as a liquidcrystal display can be used as the display 12.

Input to the input unit 13 are various kinds of information such asimaging conditions desired by an operator, the pulse sequence, andinformation regarding the synthesizing processing and differencecomputing. The input unit 13 sends the input information to the hostcomputer 6. The input unit 13 to be suitably provided is, for example, apointing device such as a mouse or a track ball, a selecting device suchas a mode change switch, or an input device such as a keyboard.

The breath-holding instructor comprises the sound generator 16. Thesound generator 16 generates messages for the start and end of breathholding as sounds under the control of the host computer 6.

The electrocardiographic measure includes the ECG sensor 17 and the ECGunit 18. The ECG sensor 17 is attached to the surface of the body of thesubject 200, and detects the ECG signal of the subject 200 as anelectric signal (hereinafter referred to as a sensor signal). The ECGunit 18 subjects the sensor signal to various processing includingdigitization, and then outputs it to the sequencer 5 and the hostcomputer 6. The sensor signal is used by the sequencer 5 when theimaging scan is performed. This makes it possible to properly setsynchronization timing by the ECG gate method (electrocardio-graphicsynchronization method), and the imaging scan of the ECG gate methodbased on this synchronization timing can be performed to collect data.

The operation of the MRI apparatus 100 configured as described abovewill next be described in detail.

First Embodiment

The first embodiment is described below. The first embodimentcorresponds to First Problem.

FIG. 2 is a diagram showing a pulse sequence in the first embodiment.Waveforms shown in FIG. 2 represent, from top to bottom, an ECG as asynchronization waveform, a radio-frequency (RF) pulse applied to animaging target, a slice direction gradient magnetic field waveform(Gss), a readout direction gradient magnetic field waveform (Gro), aphase encoding direction gradient magnetic field waveform (Gpe), and adeviation (Δf) of a carrier wave from a center frequency during theapplication of the radio-frequency pulse. A period P1 is a tag sequencepart for labeling blood or cerebrospinal fluid. A period P2 is a mainpulse sequence part for imaging. Although a fast spin echo method isemployed in this example, it is possible to use any imaging method suchas the coherent gradient echo method (the true SSFP method, true FISP orbalanced FFE method).

As apparent from a comparison between FIGS. 2 and 24, the pulse sequencein the first embodiment is based on the pulse sequence disclosed inJapanese Patent Application KOKAI Publication No. 2001-252263. That is,an imaging cycle comprising labeling in period P1 and echo collection inperiod P2 is repeated a plurality of times with variations in the sizeof an inversion time TI ranging from excitation by a labeling pulse LPto the start of the pulse sequence for the echo collection. The pulsesequence in the first embodiment is different from the pulse sequence inFIG. 24 in which a time TDtag ranging from a reference time point to theexcitation by the labeling pulse LP is changed contrary to the size ofthe inversion time TI in every imaging cycle. In addition, a time pointin which an R wave is appeared in the ECG is the reference time point.

FIG. 3 is a flowchart for the processing of the host computer 6 forcondition setting.

In step Sa1, input to the host computer 6 is the value of an inversiontime TI_(n) designated by, for example, an operator for each of theplurality of imaging cycles, or are the number of imaging cycles, thevalue of an inversion time TI₁ in the first imaging cycle and avariation ΔTI of the inversion time TI, designated by, for example, theoperator thereby calculating the inversion time TI_(n) for an n-thimaging cycle in accordance with a predetermined equation. For example,the following equation can be applied as such an equation.

TI _(n) =TI ₁−(n−1)·ΔTI

In step Sa2, input to the host computer 6 is a value designated by, forexample, the operator as a time TDseq ranging from the reference timepoint to the start of the pulse sequence for echo collection.

The various values input in step Sa1 and step Sa2 may be in any form,such as a default value or a value selected by the operator from aplurality of default values. Moreover, the various values may be inputin any order.

In step Sa3, the host computer 6 calculates a time TDtag_(n) for each ofthe plurality of imaging cycles.

TDtag _(n) =TDseq−TI _(n)

In addition, since TDtag_(n) generally has to be zero or a positivevalue for convenience of the control of the apparatus, the control maybe limited as necessary so that TDseq is equal to or more than themaximum value of TI_(n) when TDseq is input.

In step Sa4, the host computer 6 performs a scan in accordance with thepulse sequence shown in FIG. 2. At this time, the host computer 6instructs the sequencer 5 to apply the time TDtag_(n) and the inversiontime TI_(n) in the n-th imaging cycle. In accordance with thisinstruction, the sequencer 5 repetitively performs the imaging cycleswith variations in the time TDtag and the inversion time TI. In theexample in FIG. 2, while an inversion time TI₂ in the second imagingcycle is smaller than the inversion time TI₁ in the first imaging cycle,a time TDtag2 in the second imaging cycle is, on the contrary, largerthan a time TDtag1 in the first imaging cycle.

A plurality of images reconstructed on the basis of the echo datacollected in every imaging cycle are sequentially displayed such thatinformation useful to observe the dynamic state of the blood orcerebrospinal fluid can be presented. That is, portions that are notlabeled on the image show a low signal intensity because the motion ismade in accordance with a flow velocity during the inversion time TI ina part with motion among parts excited by the labeling pulse LP inperiod P1. If this part is traced on each image, the motion of the bloodor cerebrospinal fluid can be observed.

On the other hand, in the first embodiment, the time TDtag is in inverseproportion to the inversion time TI, so that the time TDseq is the samein each of the imaging cycles. Thus, while the inversion time TI ischanged to visualize the dynamic state of the blood or cerebrospinalfluid, the time TDseq ranging from the reference time point to the startof the pulse sequence for echo collection is uniform in the imagingcycles. Therefore, each of the imaging cycles accurately synchronizeswith the ECG, such that the influence of periodic changes with pulsationis held down and a change and image artifacts in each imaging can besuppressed.

When, for example, the fast spin echo method is employed that uses theCPMG pulse sequence as the main pulse sequence, an image is formed asthe composition of a plurality of echo components with different phasevariations due to flow velocities, and this leads to a sharp changes inimage values corresponding to the flow velocities due to theinterferential action of phases. Thus, the reduction of the imagevariation owing to the homogeneity of the time TDseq in the imagingcycles in accordance with the first embodiment is more evident than inother pulse sequences and is particularly effective.

In addition, it is also possible to employ a pulse sequence requiring aplurality of shots to reconstruct one image. In this case, a proceduremay be taken that repeats echo collections corresponding to the numberof shots necessary for reconstructing one image without changing theinversion time TI and further repeats this processing with variations inthe inversion time TI.

Furthermore, as shown in FIG. 4, an IR pulse (180 degree pulse) PA maybe added before the labeling pulse LP in a slice non-selection state(where a slice gradient magnetic field is zero during RF application).This brings the longitudinal magnetization of the labeled part to nearlyan initial state, so that the motion of the blood or cerebrospinal fluidcan be imaged as a high signal intensity. That is, it is possible toobtain a negative/positive inversion of the image obtained by the pulsesequence shown in FIG. 2.

Second Embodiment

The second embodiment is described below. The second embodimentcorresponds to Second Problem.

FIG. 5 is a diagram showing a pulse sequence in the second embodiment.Waveforms shown in FIG. 5 represent, from top to bottom, a cerebrospinalfluid pulsation waveform as a synchronization waveform, aradio-frequency (RF) pulse applied to an imaging target, a slicedirection gradient magnetic field waveform (Gss), a readout directiongradient magnetic field waveform (Gro), a phase encoding directiongradient magnetic field waveform (Gpe), and a deviation (Δf) of acarrier wave from a center frequency during the application of theradio-frequency pulse. A period P1 is a tag sequence part for labelingblood or cerebrospinal fluid. A period P2 is a main pulse sequence partfor imaging. Although the fast spin echo method is employed in thisexample, it is possible to use any imaging method such as the coherentgradient echo method (the true SSFP method, true FISP or balanced FFEmethod).

As apparent from a comparison between FIGS. 5 and 24, the pulse sequencein the second embodiment has periods P1 and P2 similar to those in thepulse sequence disclosed in Japanese Patent Application KOKAIPublication No. 2001-252263, and further have a period P11 before periodP1. Period P11 is a period for detecting a trigger starting period P1.Then, a time point in which the trigger is detected at period P11 is setas the reference time point so that the imaging cycle including labelingat period P1 and echo collection at period P2 is repeated a plurality oftimes.

FIG. 6 is a diagram showing a pulse sequence for trigger detection inperiod P11 in FIG. 5. Waveforms shown in FIG. 6 represent, from top tobottom, a radio-frequency (RF) pulse applied to an imaging target, aslice direction gradient magnetic field waveform (Gss), a readoutdirection gradient magnetic field waveform (Gro), a phase encodingdirection gradient magnetic field waveform (Gpe), a gradient magneticfield pulse (Gvenc) for flow encoding, and an echo signal waveform(Echo). A period P21 is a two-dimensional RF pulse for exciting acylindrical region. The excitation by the two-dimensional RF pulse isknown from Hardy, C. J., and Cline, H. E., 1989. “Broadband NuclearMagnetic Resonance Pulses with Two-dimensional Spatial Selectivity,” J.Appl. Phys 66:1513-1516.

In order to raise the time resolution of a flow velocity, the imagingregion can be limited by a two-dimensional excitation method in theslice direction and phase encoding direction to measure a limited volumeof cerebrospinal fluid or blood in one time TR. After the excitation,the gradient magnetic field pulse Gvenc for flow encoding is applieduntil the echo collection such that a phase variation proportionate toan average flow velocity during a period is produced in an echo signal.In addition, the time TR is, for example, about 10 to 200 ms.

An echo signal having a waveform such as a waveform W shown in FIG. 7can be obtained by the above-mentioned pulse sequence for triggerdetection. Then, the echo signal is subjected to one-dimensional Fouriertransformation (1DFT) by the host computer 6 such that profiles PR1 andPR2 of an absolute value and a phase in the readout direction areobtained as shown in FIG. 7.

Now, before starting imaging, set in accordance with an instruction of,for example, an operator are a region to be excited in the pulsesequence for trigger detection (hereinafter referred to as an excitationregion) and a region targeted for the observation of a phase variation(hereinafter referred to as an observation region).

FIG. 9 is a diagram showing an example of how the excitation region andthe observation region are set. In this example, the operator indicates,on a positioning image, a rectangular frame 21 representing theexcitation region and two straight lines 22 and 23 perpendicular to thereadout direction. Then, the host computer 6 sets, as the excitationregion, a columnar (bar-shaped) region whose projected shape looks likethe rectangular frame 21. Further, the host computer 6 sets theobservation region in accordance with an intermediate position r₀ in thereadout direction of the straight lines 22 and 23 and a space Δr betweenthe straight lines 22 and 23.

FIG. 10 is a diagram showing another example of how the excitationregion and the observation region are set. In this example, since thereadout direction is different from that in the example in FIG. 9, thedirections of a rectangular frame 24 and straight lines 25 and 26 aredifferent. However, no change is made in setting, as the excitationregion, a columnar (bar-shaped) region whose projected shape looks likethe rectangular frame 24 and in setting the observation region inaccordance with the intermediate position r₀ in the readout direction ofthe straight lines 25 and 26 and the space Δr between the straight lines25 and 26. In addition, the positions of the two straight lines in thereadout direction may be used as information indicating the observationregion instead of position r₀.

In addition, the positioning image in FIGS. 9 and 10 is a sagittalsectional image of a head. In this case, in the pulse sequence fortrigger detection, changes in the flow velocity of the cerebrospinalfluid in the head are directly and continuously found by an NM signal todetect a trigger. In this case, as shown in FIGS. 9 and 10, it isdesirable to set the excitation region so that the part of cerebralaqueduct with a high flow velocity and a great variation is included andto adjust a flow encoding direction to the flowing direction of thecerebrospinal fluid. Moreover, FIG. 9 shows an example in which thereadout direction is set along the part of cerebral aqueduct, and FIG.10 shows an example in which the slice direction or phase encodingdirection is set along the part of cerebral aqueduct. The example inFIG. 10 has a smaller range in which the part of the cerebrospinal fluidto be observed is excited in the pulse sequence for trigger detectionand, therefore, has an advantage that the main imaging executed afterthe trigger detection is less affected.

The host computer 6 measures an average phase variation θ(ro, i) withinthe observation region in the phase profile PR2. Note that i indicatesan index of the number of repetition of the time TR. The observationregion is set as described above such that a target voxel can besmaller, the effect of a partial volume is less, and a phase variationfaithfully reflecting the change of the flow velocity can be measured.

If the phase variation θ(ro, i) measured at every the time TR is plottedin order of time, the pulsation of the cerebrospinal fluid is shown, forexample, as in FIG. 8. Thus, a time point when the measured phasevariation θ(ro, i) coincides with a predetermined state is set as areference time point such that this reference time point accuratelysynchronizes with the pulsation of the cerebrospinal fluid. FIG. 8 showsan example wherein a time point in which the phase variation θ(ro, i)exceeds a threshold value is determined to be the reference time point.In order to determine the reference time point, it is also possible toemploy other methods such as a method that temporally differentiates awaveform, for example, as shown in FIG. 8 to detect an inflection point.However, part of data can only be collected for the phase variationθ(ro, i) after the start of imaging, and it is therefore necessary insome cases to sequentially execute the sequence for trigger detectionbefore the start of imaging to determine the intervals of an averagereference time point (trigger) or a threshold value that enables astable detection of the reference time point (trigger).

Then, as shown in FIG. 5, the host computer 6 controls the sequencer 5to repetitively perform the pulse sequence in periods P1 and P2, thatis, the main imaging in synchronization with the reference time pointdetermined in period P11 as described above. In addition, in the examplein FIG. 5, the pulse sequence in period P1 is triggered upon reachingthe reference time point.

Thus, according to the second embodiment, the pulsation of thecerebrospinal fluid is observed and the reference time point isdetermined on the basis of the result of the observation, such that itis possible to more accurately collect echoes synchronously with thepulsation of the cerebrospinal fluid than in the case where the ECG isused as the synchronization waveform. As a result, the influence ofperiodic changes with pulsation is held down and a change and artifactof the image in each imaging can be held down.

In addition, the pulse sequence for trigger detection in the secondembodiment can be applied to the sequence for imaging in, for example,the first and third embodiments.

Part (e.g., one-dimensional Fourier transformation) of the processingfor trigger detection may be carried out in the arithmetical unit 10.

While the example has been shown where a local change in the flowvelocity of the cerebrospinal fluid is targeted for the triggerdetection, it is known that cerebral parenchyma is moved by thepulsation of the cerebrospinal fluid. It is also possible to apply ahigh-intensity gradient magnetic field pulse (Gvenc) for flow encodingand target a slight motion in the part of cerebral parenchyma for thetrigger detection. It is also possible to target a change in a bloodflow for the trigger detection.

Third Embodiment

The third embodiment is described below. The third embodimentcorresponds to Second Problem.

FIG. 11 is a diagram showing a pulse sequence in the third embodiment.Waveforms shown in FIG. 11 represent, from top to bottom, anelectrocardiograph (ECG) as a synchronization waveform, aradio-frequency (RF) pulse applied to an imaging target, a slicedirection gradient magnetic field waveform (Gss), a readout directiongradient magnetic field waveform (Gro), a phase encoding directiongradient magnetic field waveform (Gpe), and a deviation (Δf) of acarrier wave from a center frequency during the application of theradio-frequency pulse. A period P1 is a tag sequence part for labelingblood or cerebrospinal fluid. A period P2 is a main pulse sequence partfor imaging. Although a fast spin echo method is employed in thisexample, it is possible to use any imaging method such as the coherentgradient echo method (the true SSFP method, true FISP or balanced FFEmethod).

As apparent from a comparison between FIGS. 11 and 24, the pulsesequence in the third embodiment is based on the pulse sequencedisclosed in Japanese Patent Application KOKAI Publication No.2001-252263. That is, an imaging cycle comprising labeling in period P1and echo collection in period P2 is repeated a plurality of times. Thepulse sequence in the third embodiment is different from the pulsesequence in FIG. 24 in which the time TDtag and the inversion time TIare constant in the respective cycles. In addition, Japanese PatentApplication KOKAI Publication No. 2001-252263 also discloses a sequencein which the time TDtag and the inversion time TI are constant in therespective cycles, but a labeling region is also the same in therespective cycles in the third embodiment while the labeling regionvaries cycle by cycle in Japanese Patent Application KOKAI PublicationNo. 2001-252263. Such a pulse sequence can be produced by the control ofthe sequencer 5.

A plurality of images reconstructed on the basis of the echo datacollected in every imaging cycle are sequentially displayed such that itis possible to only observe an image change due to a variation in themotion of an observation target during each imaging. The order ofsequentially displayed images may be replaced as necessary depending onthe distance at which a labeled portion is reached on each image.

Furthermore, in order to reduce the influence of each variation of theflow velocity, a plurality of taken images IM1, IM2, . . . , IMm areaveraged to generate and display an average image IMave, for example, asshown in FIG. 12. Alternatively, a variance image IMvar proportionate tothe variance of the images IM1, IM2, . . . , IMm may be generated anddisplayed, for example, as shown in FIG. 13. Moreover, the average imageIMave and the variance image IMvar may be superposed on each other anddisplayed with different colors.

Furthermore, a plurality of image collections as described above arecarried out in such a manner as to change the inversion time TI and thelabeling region as necessary, and a plurality of images thus obtainedare averaged, so that a series of such processing may be performed foreach of the different inversion times TI and the labeling regions atdifferent positions, and a plurality of obtained different images afteraveraging may be sequentially displayed. In this case, the influence ofeach variation of the flow velocity that has been evident in eachimaging can be significantly reduced, and an image change due to thedifference of the inversion times TI and the positions of the labelingregions can be more vividly displayed.

The various images as described above are displayed on the display 12under the control of, for example, the host computer 6. Moreover,various kinds of image processing are carried out in the host computer 6and the arithmetical unit 10.

Fourth Embodiment

The fourth embodiment is described below. The fourth embodimentcorresponds to Third Problem.

FIG. 14 is a diagram showing a pulse sequence in the fourth embodiment.Waveforms shown in FIG. 14 represent, from top to bottom, anelectrocardiograph (ECG) as a synchronization waveform, aradio-frequency (RF) pulse applied to an imaging target, a slicedirection gradient magnetic field waveform (Gss), a readout directiongradient magnetic field waveform (Gro), a phase encoding directiongradient magnetic field waveform (Gpe), and a deviation (of) of acarrier wave from a center frequency during the application of theradio-frequency pulse. A period P31 is a tag sequence part for labelingblood or cerebrospinal fluid. A period P2 is a main pulse sequence partfor imaging. Although a fast spin echo method is employed in thisexample, it is possible to use any imaging method such as the coherentgradient echo method (the true SSFP method, true FISP or balanced FFEmethod).

In the pulse sequence in the fourth embodiment, an imaging cyclecomprising labeling in period P31 and echo collection in period P2 isrepeated a plurality of times. The pulse sequence for the echocollection in period P2 is similar to that shown in FIG. 24.

In period P31, three labeling pulses LP₁, LP₂ and LP₃ are sequentiallyapplied from a time point when a time TDtag has passed from a referencetime point in which an R wave is produced in the ECG. When labelingpulses LP₁ to LP₃ are applied, the gradient magnetic field waveform isvaried as shown in FIG. 14 to vary the labeling region. Further, alabeling pulse LP₀ is applied before the application of labeling pulseLP₁. At this time, no gradient magnetic field is generated and thelabeling region is nonselective. Such a pulse sequence can be producedby the control of the sequencer 5.

The region excited by any one of labeling pulses LP₁ to LP₃ is alsoinversely excited 180 degrees by labeling pulse LP₀. Since the timedifference between labeling pulse LP₀ and labeling pulse LP₁, LP₂ or LP₃is short enough for a T1 value of a labeling target such as thecerebrospinal fluid, the regions excited by labeling pulses LP₁ to LP₃are in a condition similar to having been excited at a flip angle of 360degrees, and the longitudinal magnetization is substantially in theinitial state. On the other hand, the region that is not excited by anyone of labeling pulses LP₁ to LP₃ is only excited by labeling pulse LP₀,and is, therefore, excited at 180 degrees, and the longitudinalmagnetization is inverted.

Thus, according to the pulse sequence in the fourth embodiment, threedifferent regions can be labeled. Further, labeled portions in theabove-mentioned three regions alone show a high signal intensity in animage reconstructed from the echoes collected in period P2. That is,according to the image taken by the fourth embodiment, it is possible toknow the dynamic state of the cerebrospinal fluid or blood in a widerange on one image and conduct an efficient inspection.

Furthermore, as the independent three regions can be labeled, it ispossible to obtain an image effective in knowing the dynamic state ofthe cerebrospinal fluid or blood in different parts.

In addition, it is also possible to provide two labeling regions, orfour or more labeling regions.

A specific example of how to set a plurality of labeling regions isdescribed below.

Monro foramen, cerebral aqueduct and pontine cistern, foramen magnum,etc. are known to be clinically highly interested parts. In these parts,a portion in which the cerebrospinal fluid flows is narrow even in anormal healthy person, and a flow velocity is relatively high. In somecases, these parts become narrower than those of the normal healthypersons, or the flow of the cerebrospinal fluid changes. Therefore, asshown in, for example, FIG. 15, it is possible to designate, as labelingregions, a region R1 including Monro foramen, a region R2 includingcerebral aqueduct and pontine cistern, and a region R3 including foramenmagnum. The clinical knowledge of the circulatory pathways of thecerebrospinal fluid or blood is used to properly set the three labelingregions in this manner, such that it is possible to obtain an extremelyuseful image suitable to a clinical observation purpose.

Fossa lateralis cerebri is known to be another clinically highlyinterested part. When it is intended to know the dynamic state of thecerebrospinal fluid in fossa lateralis cerebri, it is desirable to set asection S1 that shows a sagittal image substantially closed to a coronalimage and that passes in the vicinity of anterior commisure or opticchiasm, for example, as shown in FIG. 16. FIG. 17 is a diagram showing atwo-dimensional (2D) image taken in section S1. Then, as shown in FIG.17, labeling regions R11 and R12 are set on the two-dimensional image,and imaging is performed by the pulse sequence described above, suchthat, for example, an image as shown in FIG. 18 can be obtained. Inportions with sufficiently less motion during imaging, labeling regionsR11 and R12 during imaging as such show a high signal intensity. Due tothe motion of the cerebrospinal fluid, the cerebrospinal fluid shows ahigh signal intensity in regions R13 to R17. This means that thecerebrospinal fluid is horizontally moving to and fro (“to-and-fromotion”) in fossa lateralis cerebri. On the other hand, in general, ahigh signal intensity is rarely observed in regions R17 and R18. Bymaking a comparison between the ranges of the high-signal-intensityparts, between right and left sides or between conditions before andafter a treatment, diagnostically necessary information can becollected, so that it is useful to set a plurality of labeling regionssuch as labeling regions R11 and R12.

Fifth Embodiment

The fifth embodiment is described below. The fifth embodimentcorresponds to Fourth Problem.

The host computer 6 displays an image, for example, as shown in FIG. 19taken after labeling as a positioning image on the display 12, andinstructed by an operator on the designation of a section on this image.In addition, in FIG. 19, a region 21 is designated as a labeling region,and a region 22 is visualized with a high signal intensity. Moreover, itis possible to apply any pulse sequence for taking the positioning imagesuch as those shown in the embodiments described above or JapanesePatent Application KOKAI Publication No. 2001-252263.

Thus, the operator can decide an imaging section S11 including a portionwith a high flow velocity of the cerebrospinal fluid, for example, asshown in FIG. 20.

FIG. 21 shows a two-dimensional image taken in imaging section S11. Ifsuch an image is taken after being provided with a labeling region R23including Monro foramen as shown in FIG. 21, an image, for example, asshown in FIG. 22 can be obtained. A shaded region R24 is where thecerebrospinal fluid has moved from labeling region R23 after labeling,and shows a high signal intensity. That is, the image shown in FIG. 22is taken by the pulse sequence that applies a nonselective IR pulsebefore a labeling pulse as shown in FIG. 4.

This permits a setting to be made after information on the flow of thecerebrospinal fluid has been known, so that it is possible to moreeasily set an imaging section in a part with a fast flow of thecerebrospinal fluid or in a diagnostically interested position ordirection than when an imaging section is set with a normal positioningimage.

Sixth Embodiment

The sixth embodiment is described below. The sixth embodimentcorresponds to Fifth Problem.

FIG. 23 is a flowchart for the characteristic processing of the hostcomputer 6 in the sixth embodiment.

The host computer 6 is instructed on the designation of a labelingregion as a preparation of an inspection. At this time, it is desirableto properly designate the labeling region in accordance with diagnosticpurposes and other imaging conditions by taking advantage of clinicalknowledge of the circulatory pathways of the cerebrospinal fluid orblood.

When the labeling region is designated, the host computer 6 generateslabeling position information on the designated labeling region in stepSb1. The labeling position information includes information such asoffset, rotation information, the width of the labeling region and thekind and duration of an RF pulse. In step Sb2, the host computer 6 savesthe generated labeling position information in a labeling positionstorage.

As the labeling position storage, it is possible to use any storagemedium such as the storage unit 11, a storage medium managed by anin-hospital server connected to the MRI apparatus 100 in the sixthembodiment via an in-hospital network, or a storage medium managed by aWeb server connected to the MRI apparatus 100 in the sixth embodimentvia, for example, the Internet.

During an actual inspection, the host computer 6 reads the labelingposition information from the labeling position storage in step Sc1.Then, in step Sc2, the host computer 6 sets a labeling region on thebasis of the labeling position information.

Thus, the labeling region can be easily and properly set during theactual inspection even by an operator of the apparatus who has noclinical knowledge of the circulatory pathways of the cerebrospinalfluid or blood, so that variations in image quality due to the level ofskills of the operators of the apparatus can be reduced.

In addition, the labeling position information regarding severallabeling regions may be saved in advance in the labeling positionstorage, and this labeling position information may be selectively readand used to set the labeling regions. This requires no designation ofthe labeling region as the preparation of the inspection and makes theoperation simpler.

Various modifications such as those mentioned below can be made in theembodiments described above.

Other biological signals such as a sphygmographic signal can be usedinstead of the ECG or the signal indicating the pulsation of thecerebrospinal fluid.

A proper combination of the plurality of embodiments described above canbe carried out.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A magnetic resonance imaging apparatus which generates a magneticresonance image on the basis of an echo signal regarding a spin includedin an imaging region of a subject, the apparatus comprising: an imagingunit which applies a labeling pulse to invert the spin included in alabeling region within part of the imaging region and then applies anexcitation pulse at a time point when an inversion time has passed fromthe application of the labeling pulse in order to collect the resultingecho signal; and a control unit, the control unit controlling theimaging unit so that the echo signal in the imaging region is collecteda plurality of times with variations in the inversion time, the controlunit also controlling the imaging unit so that a time ranging from areference time point within a biological signal obtained from thesubject to the application of the excitation pulse is constantregardless of the inversion time in the plurality of collections of theecho signal.
 2. A magnetic resonance imaging apparatus comprising: anacquisition unit which acquires an echo signal regarding a spin includedin an imaging region of a subject in accordance with a predeterminedpulse sequence; a reconstruction unit which reconstructs an image of theinside of the imaging region in accordance with the acquired echosignal; a labeling unit which inverts the spin included in a labelingregion within part of the imaging region to conduct labeling; and acontrol unit, the control unit controlling the labeling unit and theacquisition unit so that a cycle of conducting the labeling andacquiring the echo signal from a time point when a given first time haspassed from a time point of the labeling is carried out a plurality oftimes without changing the labeling region, the control unit alsocontrolling the labeling unit and the acquisition unit so that each ofthe plurality of cycles is started at a time point when a given secondtime has passed from a periodic reference time point.
 3. The magneticresonance imaging apparatus according to claim 2, further comprising: aunit which generates a composite image of at least two of imagesreconstructed by the reconstruction unit on the basis of the echo signalacquired in each of the plurality of cycles.
 4. The magnetic resonanceimaging apparatus according to claim 2, further comprising: a unit whichcalculates the moving distance of the labeled spin on the basis of atleast two images of interest out of images reconstructed by thereconstruction unit in accordance with the echo signal acquired in eachof the plurality of cycles, and sequentially displays the images ofinterest in an order corresponding to the calculated moving distance. 5.The magnetic resonance imaging apparatus according to claim 2, whereinthe control unit decides the reference time point on the basis of asynchronization signal.
 6. The magnetic resonance imaging apparatusaccording to claim 5, wherein the control unit uses anelectrocardiographic signal regarding the subject as the synchronizationsignal.
 7. A magnetic resonance imaging apparatus comprising: anacquisition unit which acquires an echo signal regarding a spin includedin an imaging region of a subject in accordance with a predeterminedpulse sequence; a reconstruction unit which reconstructs an image of theinside of the imaging region in accordance with the acquired echosignal; a labeling unit which inverts the spin included in a labelingregion within part of the imaging region to conduct labeling; anobservation unit which repetitively acquires a magnetic resonance signalfrom within the labeling region and observes a change of the flowvelocity of a fluid in the labeling region on the basis of a change ofthe repetitively acquired magnetic resonance signal; and a control unit,the control unit controlling the labeling unit and the acquisition unitso that a cycle of conducting the labeling and acquiring the echo signalfrom a time point when a predetermined first time has passed after thelabeling is carried out a plurality of times, the control unit alsocontrolling the labeling unit and the acquisition unit so that the cycleis started at a time point when a predetermined second time has passedfrom a reference time point at which the observed change of the flowvelocity coincides with a predetermined state.
 8. The magnetic resonanceimaging apparatus according to claim 7, wherein the observation unitonly acquires the magnetic resonance signal from an observation regionwithin part of the labeling region.
 9. The magnetic resonance imagingapparatus according to claim 7, wherein the observation region is acerebral aqueduct.
 10. A magnetic resonance imaging apparatuscomprising: an acquisition unit which acquires an echo signal regardinga spin included in an imaging region of a subject in accordance with apredetermined pulse sequence; a reconstruction unit which reconstructsan image of the inside of the imaging region in accordance with theacquired echo signal; a labeling unit which inverts the spin included inthe imaging region and then inverts the spin included in each of aplurality of labeling regions within part of the imaging region toconduct labeling; and a control unit, the control unit controlling thelabeling unit and the acquisition unit so that a cycle of conducting thelabeling and acquiring the echo signal from a time point when apredetermined first time has passed from a time point of the labeling iscarried out a plurality of times, the control unit also controlling thelabeling unit and the acquisition unit so that the cycle is started at atime point when a predetermined second time has passed from a periodicreference time point.
 11. A magnetic resonance imaging apparatuscomprising: an acquisition unit which acquires an echo signal regardinga spin included in an imaging region of a subject in accordance with apredetermined pulse sequence; a reconstruction unit which reconstructsan image of the inside of the imaging region in accordance with theacquired echo signal; a labeling unit which inverts the spin included ina labeling region within part of the imaging region to conduct labeling;a control unit, the control unit controlling the labeling unit and theacquisition unit so that a cycle of conducting the labeling andacquiring the echo signal from a time point when a predetermined firsttime has passed after the labeling is carried out a plurality of times,the control unit also controlling the labeling unit and the acquisitionunit so that each of the plurality of cycles is started at a time pointwhen a predetermined second time has passed from a periodic referencetime point; a unit which displays, as a positioning image, one of theplurality of images reconstructed on the basis of the echo signalacquired in each of the plurality of cycles; and a unit which accepts adesignation of an imaging section on the positioning image.
 12. Amagnetic resonance imaging apparatus having access to a storage device,the apparatus comprising: an acquisition unit which acquires an echosignal regarding a spin included in an imaging region of a subject inaccordance with a predetermined pulse sequence; a reconstruction unitwhich reconstructs an image of the inside of the imaging region inaccordance with the acquired echo signal; a labeling unit which invertsthe spin included in a labeling region within part of the imaging regionto conduct labeling; a control unit, the control unit controlling thelabeling unit and the acquisition unit so that a cycle of conducting thelabeling and acquiring the echo signal from a time point when apredetermined first time has passed after the labeling is carried out aplurality of times, the control unit also controlling the labeling unitand the acquisition unit so that each of the plurality of cycles isstarted at a time point when a predetermined second time has passed froma periodic reference time point; and a unit which sets the labelingregion on the basis of information stored in the storage device.
 13. Themagnetic resonance imaging apparatus according to claim 12, includingthe storage device therein.
 14. The magnetic resonance imaging apparatusaccording to claim 12, further comprising: a unit which saves, in thestorage device, information indicating the labeling region set on thebasis of an instruction of a user.
 15. A magnetic resonance imagingmethod which generates a magnetic resonance image on the basis of anecho signal regarding a spin included in an imaging region of a subject,the method comprising: applying a labeling pulse to invert the spinincluded in a labeling region within part of the imaging region and thenapplying an excitation pulse at a time point when an inversion time haspassed from the application of the labeling pulse in order to collectthe resulting echo signal; and controlling the application of thelabeling pulse and the collection so that the echo signal in the imagingregion is collected a plurality of times with variations in theinversion time, and also controlling the application of the labelingpulse and the collection so that a time ranging from a reference timepoint within a biological signal obtained from the subject to theapplication of the excitation pulse is constant regardless of theinversion time in the plurality of collections of the echo signal.
 16. Amagnetic resonance imaging method comprising: acquiring an echo signalregarding a spin included in an imaging region of a subject inaccordance with a predetermined pulse sequence; inverting the spinincluded in a labeling region within part of the imaging region toconduct labeling; controlling the labeling and the acquisition so that acycle of conducting the labeling and acquiring the echo signal from atime point when a given first time has passed from a time point of thelabeling is carried out a plurality of times without changing thelabeling region, and also controlling the labeling and the acquisitionso that each of the plurality of cycles is started at a time point whena given second time has passed from a periodic reference time point; andreconstructing an image of the inside of the imaging region inaccordance with the acquired echo signal.
 17. A magnetic resonanceimaging method comprising: acquiring an echo signal regarding a spinincluded in an imaging region of a subject in accordance with apredetermined pulse sequence; inverting the spin included in a labelingregion within part of the imaging region to conduct labeling;repetitively acquiring a magnetic resonance signal from within thelabeling region and observing a change of the flow velocity of a fluidin the labeling region on the basis of a change of the repetitivelyacquired magnetic resonance signal; controlling the labeling and theacquisition so that a cycle of conducting the labeling and acquiring theecho signal from a time point when a predetermined first time has passedafter the labeling is carried out a plurality of times, and alsocontrolling the labeling and the acquisition so that the cycle isstarted at a time point when a predetermined second time has passed froma reference time point at which the observed change of the flow velocitycoincides with a predetermined state; and reconstructing an image of theinside of the imaging region in accordance with the acquired echosignal.
 18. A magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; inverting the spinincluded in the imaging region and then inverting the spin included ineach of a plurality of labeling regions within part of the imagingregion to conduct labeling; and controlling the labeling and theacquisition so that a cycle of conducting the labeling and acquiring theecho signal from a time point when a predetermined first time has passedfrom a time point of the labeling is carried out a plurality of times,and also controlling the labeling and the acquisition so that the cycleis started at a time point when a predetermined second time has passedfrom a periodic reference time point; reconstructing an image of theinside of the imaging region in accordance with the acquired echosignal.
 19. A magnetic resonance imaging method comprising: acquiring anecho signal regarding a spin included in an imaging region of a subjectin accordance with a predetermined pulse sequence; inverting the spinincluded in a labeling region within part of the imaging region toconduct labeling; controlling the labeling and the acquisition so that acycle of conducting the labeling and acquiring the echo signal from atime point when a predetermined first time has passed after the labelingis carried out a plurality of times, and also controlling the labelingand the acquisition so that each of the plurality of cycles is startedat a time point when a predetermined second time has passed from aperiodic reference time point; reconstructing an image of the inside ofthe imaging region in accordance with the acquired echo signal;displaying, as a positioning image, one of the plurality of imagesreconstructed on the basis of the echo signal acquired in each of theplurality of cycles; and accepting a designation of an imaging sectionon the positioning image.
 20. A magnetic resonance imaging method in amagnetic resonance imaging apparatus having access to a storage device,the method comprising: acquiring an echo signal regarding a spinincluded in an imaging region of a subject in accordance with apredetermined pulse sequence; inverting the spin included in a labelingregion within part of the imaging region to conduct labeling;controlling the labeling and the acquisition so that a cycle ofconducting the labeling and acquiring the echo signal from a time pointwhen a predetermined first time has passed from a. time point of thelabeling is carried out a plurality of times, and also controlling thelabeling and the acquisition so that each of the plurality of cycles isstarted at a time point when a predetermined second time has passed froma periodic reference time point; setting the labeling region on thebasis of information stored in the storage device; and reconstructing animage of the inside of the imaging region in accordance with theacquired echo signal.